Natural Science

MODULE 10: Sources of Energy

Key words

Unit 1: Non-renewable sources of energy

A fossil fuel is non-renewable because it took millions of years to form and cannot be replenished. Burning a fuel converts its chemical energy to heat energy, but also releases polluting gases.

Coal

•      Formed when plants in swamps died millions of years ago and were buried under sand and rock.

•      The weight of the layers created high pressure, turning the dead plant material into peat.

•      Peat was pushed toward the hot centre of the Earth — the heat changed it into coal (the other substances became oil and gas).

•      Coal can be mined open-cast (if near the surface) or from underground.

•      Burnt to generate electricity — more than half the world's coal is used this way.

Oil

•      Crude oil and natural gas are often found together underground.

•      Extracted by drilling into the ground; crude oil and gas rise to the top and are stored.

•      Crude oil is refined to make petrol, diesel, jet fuel and plastic products.

•      Can be burnt to generate electricity.

•      🇿🇦 South Africa fact: Sasol pioneered making petrol, diesel and other oil products from coal rather than oil — important because there is more coal than oil on Earth (though coal is also non-renewable).

Gas

•      Natural gas is pumped from underground, then processed so it can be used as a fuel.

•      Stored in gas bottles for home use, connected to lighting, heating and cooking equipment (e.g. a Bunsen burner).

•      Some countries have a national gas supply piped directly to households.

•      Can also be used to generate electricity.

Nuclear fuels (Uranium)

•      Uranium is an element used as a nuclear fuel — it contains nuclear energy (just as fossil fuels contain chemical energy).

•      Nuclear fuels convert nuclear energy into heat energy without being burnt.

•      This conversion happens in a nuclear reactor; the heat given off is eventually converted into electrical energy.

•      Koeberg Nuclear Power Station (near Cape Town) is South Africa's only nuclear power station, with two reactors. SA generates just over 5% of its electricity this way.

•      Nuclear energy does not cause air pollution, but its waste products are dangerous to human, animal and plant life and are difficult to get rid of.

•      Uranium must be mined (similar environmental impact to gold mining) — this is why nuclear energy is classified as non-renewable.

Unit 2: Renewable sources of energy

Renewable sources of energy are continually replenished, so they cannot be used up.

Hydropower

•      The use of moving water for energy.

•      Water is constantly replenished through the water cycle, making it renewable.

•      In a hydroelectric power station, moving water turns a turbine (large blades, like a fan), which provides energy to a generator that generates electricity.

Energy from wind

•      The movement of wind can be converted into other forms of energy.

•      Wind cannot be used up, so it is renewable.

•      Windmills have long been used on farms to pump groundwater; wind turbines generate electricity.

•      Large wind farms are built near the coast, where it is windy.

Energy from sunlight

•      Energy from the sun is called solar energy.

•      Solar panels (made of tiny photocells) absorb sunlight and convert it into electrical energy — used immediately or stored in a battery.

•      Heat from solar energy can also heat water in a solar water heater.

•      The sun is expected to shine for about 5 billion more years, so solar energy is considered renewable.

Biofuel

•      Biofuels come from plants.

•      Liquid biofuel (e.g. from maize or soybeans) is fermented so the sugars turn into ethanol, used as a fuel on its own or added to petrol/diesel.

•      Biogas (mainly methane) comes from waste breaking down in landfills — used as an energy source like natural gas.

•      Wood is also a biofuel — cheap, accessible, and releases heat when burnt.

•      Biofuel is renewable because crops can be replanted each year and humans constantly produce waste (for biogas).

 MODULE 11: Potential and Kinetic Energy

Key words

Unit 1: Potential energy

‘Potential’ means something that is not happening now, but is likely to happen in future. Scientifically, potential energy is energy that is stored in a system — you cannot see its effects, but the energy is there, waiting to be released.

•      A stretched elastic band has potential energy — the more you stretch it, the more potential energy it has. Once released, the energy changes into a different form (it is not lost).

•      A pen balanced on the edge of a desk has stored energy, released if it is bumped. An object of greater mass (e.g. a suitcase) in the same position would have more potential energy.

•      Batteries/cells have chemical potential energy when not connected in a circuit.

•      Fuels such as petrol, diesel, biofuel and wood all have potential energy — changed into heat energy when burnt.

Potential energy in food

•      Food has potential energy that is released in your body when you eat it — listed on packaging as the energy value.

•      Energy is measured in joules (J); food energy is usually given in kilojoules (kJ) (1 kJ = 1 000 J).

•      By law: a food is ‘low in energy’ if it has less than 170 kJ per 100 g (solids) or 80 kJ per 100 ml (liquids); ‘high in energy’ if it has more than 950 kJ per 100 g or 250 kJ per 100 ml.

Unit 2: Kinetic energy

Kinetic energy is the energy an object has when it is in motion (moving). For an object to have kinetic energy, it must be moving or changing in some way.

•      When the elastic band is released, its potential energy decreases and its kinetic energy increases as it snaps back or moves away.

•      An apple balancing on a desk has high potential energy, no kinetic energy. Once bumped and falling, the potential energy is released and changes into kinetic energy.

•      The energy in moving wind or water is kinetic energy. You may not always see the movement (e.g. electric current), but you will notice a change it causes — like a lamp glowing or a buzzer sounding.

Unit 3: Potential & kinetic energy in mechanical systems

A mechanical system needs energy to move its parts, leading to a change in the system, e.g. scissors cutting paper, or riding a bicycle.

Example — riding a bicycle:

•      Where does the input energy come from? From the man's body (legs and feet) — potential energy.

•      Where does the energy go? Legs/feet move the pedals → pedals turn the cog and chain → chain turns the rear cog → turns the rear wheel.

•      What changes are observed? The bicycle parts move, propelling the man and bicycle forward — kinetic energy.

(energy flows left → right)

Unit 4: Energy systems & the law of conservation of energy

To analyse any energy system, ask:

•      Where does the input energy come from? (the potential energy that starts the transfer)

•      Where does the energy go? (how it is transferred — may involve more than one step)

•      What energy changes are observed? (how potential energy changes into kinetic energy you can see, feel or hear)

Example — a torch: the battery's chemical potential energy converts into electrical energy, which passes through the wires and lights the bulb (giving off light energy).

Example — a wind-up radio: converts mechanical energy into electrical energy, producing sound energy.

Unit 5: Potential & kinetic energy in thermal systems

Thermal systems involve the transfer of heat energy, e.g. a pot of soup heating on a stove.

(energy flows left → right)

Unit 6: Potential & kinetic energy in electrical systems

In an electrical system, energy from an energy source causes an electric current to flow through a circuit. Electrical energy can convert into many other forms of energy.

(energy flows left → right)

•      Note: it may sound strange, but electric current flows when the switch is closed — a closed path lets current flow from the source, around the circuit, and back again.

Unit 7: Potential & kinetic energy in biological systems

Humans, animals and plants need energy to move, grow, think and sustain bodily processes — this is biological energy, which is part of a larger system that starts with the sun.

(energy flows left → right)

MODULE 12: Heat Transfer

When something is heated, heat energy is transferred from a hotter body to a cooler body until both reach the same temperature. There are three ways heat can be transferred: conduction, convection or radiation.

Unit 1: Conduction

Conduction is heat transfer between two objects in direct physical contact (touching) — heat moves from the hotter to the cooler object. Conduction can also occur within one object, as heat moves from a hotter part to a cooler part of the same object.

•      E.g. a candle heating one end of a metal rod — heat travels along the rod until it's a warm temperature overall.

•      E.g. a spoon left in hot tea gets hot — heat is transferred to the spoon by conduction.

•      Good conductors (mostly metals) conduct heat quickly — useful for pots, so heat reaches the food.

•      Poor conductors (e.g. plastic, wood) are called heat insulators — useful for pot handles, which must stay cool to touch.

Unit 2: Convection

Convection is the transfer of heat from one place to another by the movement of liquid or gas particles — called a convection current. Convection can only happen in fluids (liquids and gases).

•      When air or water is heated, it expands and the particles move upward (hot rises). When it cools, the particles move down (cool sinks).

•      Practical use: heaters work best placed near the floor (heat rises and circulates); air conditioners work best placed near the ceiling (cool air sinks).

Unit 3: Radiation

Radiation is heat transfer that needs no direct contact (unlike conduction) and no movement of particles (unlike convection) — it carries heat energy across empty space, as waves, in all directions.

•      E.g. everyone standing around a fire feels its heat equally, because the heat radiates in all directions.

•      The sun transfers heat to Earth by radiation. The Earth absorbs about half of this heat and reflects the rest back into space.

Absorption and reflection of radiated heat

•      The darker a material's colour, the more heat it absorbs. The lighter the colour, the more heat it reflects. Black absorbs the most; white reflects the most.

•      A shiny surface reflects heat; a matt surface absorbs heat — so radiation heats dark, matt surfaces fastest.

MODULE 13: Insulation and Energy Saving

Unit 1: Heat loss and gain

Energy isn't really ‘lost’ — when heat ‘loss’ happens, the heat has simply been transferred elsewhere, often into the surrounding air. Heat loss can occur through conduction, convection and radiation.

•      Electric geysers switch on when water temperature drops. Many have only thin insulation, so heat is lost by conduction through the casing, then radiation into the surroundings, and further loss by convection as hot air around the geyser rises.

•      Homes made of corrugated iron (a good conductor) get very hot in summer and very cold in winter.

•      A solar water heater uses the same principles to gain heat: it absorbs radiated heat from the sun and heats water by convection. The heated water is stored in a heavily insulated tank to avoid losing heat by conduction and radiation.

•      Tip: insulators keep cold things cold and hot things hot — a geyser blanket saves electricity.

Unit 2: Using insulating materials

Insulating materials are good for keeping cold things cold (slow heat transfer in from the surroundings) and hot things hot (slow heat transfer out to the surroundings).

•      Houses are often built from brick and concrete (poor conductors) so heat isn't easily conducted through the walls. Glass is also a poor conductor — a suitable window material.

•      Ceilings: a thick layer of insulation above the ceiling boards stops warm air escaping through the roof, forcing it to recirculate by convection.

•      Cool boxes: made from Styrofoam/plastic — spongy materials trap little bubbles of air, and air is a good insulator.

•      Vacuum flasks use the best insulator of all — a vacuum (no air at all).

•      Clothing: coats, jerseys and woolly hats prevent body heat loss. Fluffy fabrics trap a layer of air around the body.

Indigenous building design

•      South Africa is sunny and hot in summer, but cold in many parts during winter — indigenous builders design homes to stay cool in summer and warm in winter.

•      Thatched roofs: grass layered and woven together — a good insulator if well made, and relatively easy to obtain.

•      Cone-shaped roofs: hot air rises by convection into the top of the cone, keeping the room below as cool as possible.

•      Cow dung/mud mixtures are sometimes compacted onto floors (and even walls) as a traditional insulating technique.

Conserving heat energy in the home

•      Warm air escapes through gaps or cracks in ceilings, windows and door frames. Sealing cracks and using thick curtains help conserve heat energy.

MODULE 14: Energy Transfer to Surroundings

Energy cannot be destroyed, but it can be wasted. Energy wastage happens when some input energy is converted into energy that isn't needed (e.g. heat), or transferred to an object that doesn't need it.

Unit 1: Useful and wasted energy

•      Appliances/tools (irons, kettles, radios, drills) need input energy to provide a useful output. E.g. an iron: electrical → heat. A radio: electrical → sound. A car: chemical (petrol) → kinetic.

•      During energy transfer, some energy always escapes to the surroundings as wasted energy — often heat or sound.

Example: an electric drill

An electric drill converts electrical energy into kinetic energy as it turns. The output kinetic energy is less than the input electrical energy, because some is wasted as heat (the drill gets hot) and sound (the drill makes noise).

(energy flows left → right)

•      In a flow diagram, the output arrow is drawn smaller than the input arrow, since some energy was wasted (shown as separate heat + sound arrows).

Examples of energy wastage

•      Car: wastes ~65% of petrol's chemical energy — mostly as heat (to car parts & the exhaust), some as sound.

•      Coal power station: up to 50% of the energy released from burning coal is wasted as heat to the surroundings.

•      Incandescent bulb: ~90% of electrical energy wasted as heat — only 10% becomes light (poor energy efficiency).

•      CFL (energy-saving) bulb: only ~30% wasted as heat — much more energy efficient, and needs less electricity input.

MODULE 15: The National Electricity Supply System

Unit 1: Energy transfers in the national grid

Generating electricity from energy sources

Many energy sources can generate electricity — coal, oil, gas, nuclear material, falling water and wind (Module 10). This unit focuses on coal-fired power stations.

(energy flows left → right)

•      A turbine has vanes (like a fan) fitted to a circular structure. When steam hits the vanes, kinetic energy is transferred from the moving steam to the turbine, which turns rapidly.

•      In the generator, the turbine's shaft is connected to a large magnet, which spins inside a large coil of conducting cable — converting mechanical energy into electrical energy.

•      After passing through the turbine, the steam still needs to be cooled. It passes through a condenser filled with cold water, which condenses it back into a liquid.

•      This cooling process releases a lot of wasted heat energy — seen as steam rising from a power station's cooling towers. The cooled liquid is pumped back into the boiler furnace and the process starts again.

Electricity transmission and distribution

Once generated, electricity must reach consumers — this is transmission and distribution.

•      Transmission starts immediately after generation: electricity travels along conducting cables hanging from large pylons, across long distances.

•      The electricity reaches a distribution substation, and the distribution phase begins — electricity is distributed to mini substations, ready to reach households.

•      Electricity enters a house at the circuit board, then travels via conducting cables to plug points, lights and appliances.

•      Throughout transmission and distribution, transformers change the voltage of the electricity flow so that it can be distributed over large distances more efficiently.

(energy flows left → right)

Dynamos

A dynamo is a small generator that converts mechanical kinetic energy into electrical energy. Dynamos are used in tools and appliances that require only a small current.

•      E.g. a bicycle dynamo: the cyclist's pedalling motion provides the input (kinetic) energy to power a light.

•      E.g. mine helmet lights, and wind-up radios/torches: winding a crank or shaking the device provides kinetic energy → the dynamo converts it to electrical energy → then to sound (radio) or light (torch) energy.

•      Wind-up appliances with dynamos are especially useful where there is no electricity supply, or when supply is cut off after a disaster (e.g. wind-up torches and radios distributed after the 2010 Haiti earthquake).

Unit 2: Conserving electricity in the home

South Africa has a limited supply of electrical energy, so it's important not to waste it. Tips for reducing electricity waste:

•      Turn off appliances completely at the wall plug when not in use — 'stand-by' mode still uses electricity.

•      Turn off lights when they're not needed; use energy-saving (CFL) light bulbs.

•      Boil only as much water as you need in the kettle.

•      Choose solar power where possible — e.g. solar water heaters, or solar panels to charge a battery for lighting.

•      Insulate your house: seal gaps around windows, doors and between the ceiling and walls, to reduce heat escaping by convection.

•      Wear warm clothing rather than switching on a heater — it's more efficient to insulate your own body heat.

•      Match pot size to the stove plate — a stove plate larger than the pot wastes heat to the surroundings.

Careers in electricity power generation

•      Artisans (e.g. instrument technicians, electricians, boilermakers, fitters) have practical skills in a specific trade; technicians operate and maintain technical equipment.

•      Electrical engineers design new power stations, substations and distribution networks; civil engineers are essential in designing hydroelectric power stations.

•      Energy auditors track a company's energy usage and identify ways to reduce it.

•      Scientists and researchers investigate sustainable and renewable energy solutions, helping improve generation, transmission and distribution.

•      Line technicians install and repair equipment throughout the transmission and distribution network.